Autocollimating reflector and ap



Feb. 6, 1934.

H. CHRETIEN NG REFLECTOR NALING Fil LLIMATI AND APPLICATION TO CAL SIG AND NIGHT A SING Original ed Nov. 1'?

DVER'I'I 1924 Reissued' Feb. 6, 1934 UNITED STATES PATENT OFFICE AUTOCOLLIMATING REFLECTOR AND AP- PLICATION TO OPTICAL SIGNALING AND NIGHT ADVERTISING Henri Chrtien, Sit-Cloud, France, assignor, by

mes'ne assignments, to Libbey-Cataphote Corporation, Toledo, Ohio, a corporationof Ohio Original No. 1,706,218, dated March 19, 1929,

Serial No. 750,420; November 17, France November 26, reissue March 9, 1931.

13 Claims.

advantage; the adjustment of the perpendicu- I larity of the mirrors is very delicate and must be made frequently, especially for transportable To overcome that difficulty, the j lenses.

instruments. triple mirror has been made in the shape of a trirectangle tetrahedron cut out of a block of glass. But such an instrument is dilficult of construction. expensive and relatively heavy. Furthermore, the divergency of the emergent beam (or of the beam, when the apparatus is not exactly adjusted) is always very small, which renders it unusable for most of the practical applications here considered. 1

Another scheme known for a long time is the autocollimating sight invented by Fizeau, and

' which consists of an astronomical lens combined with a small plane mirror placed at its focus orthogonally to its optical axis; If such a combination is illuminated with a beam .of light emanating from a source located far away, the lens gives an image of it at the focus, that is to say on the mirrors plane. The. mirror sends the rays back, and those rays, after getting once more through the lens go back accurately to the source, even if the mirror is not perfectly perpendicular to the optical axis.

The autocollimating sight such as Fizeau conceived it, is not suitable for optical signalling, because partly of its size and partly because of the smallness of its field.

This invention aims to improve this known scheme and comprises:-

i 1. Improving the autocollimating scheme of Fizeau in order to render it usable for optical signaling.

- II. Introducing a divergency of any given amount in the emerging beam, so as to make the same observable from, a region of chosen size all around the source of light.

III. Making autocollimating reflecting surfaces of any size and shape, by assembling simple elements of autocollimating reflectors.

embodying my invention, and a 1924, and in 1923. Application for Serial No. 521,317

IV. Application of those surfaces to optical signaling in general and to night advertising in particular. I

Referring to the drawing in which like parts are similarly designated.

Figure 1 is a section showing a composite lens embodying my invention corrected astigmatically and for curvature of field. I

Fig. 2 is a similar view showing the use of mirrors.

Fig. 3 shows a single lens.

Fig. Ashows a limit of shape having lens and reflector of like curvature. ;,;-Figs.;5, 6 and '7 show different forms of lenses 8 shows diagrammatically a group Improvements in" the autocollimdting scheme of Fizeau' The objective system can be here constituted by. an ordinary type of astronomical lens, but of focal length reduced as much as possible.

.In case of application to secret optical signaling, where thedivergency must be at minima,

it'is important that the objective lens be well corrected of the spherical aberration for utilizationon the axis, and of the coma flare for utilization out of the axis. Y

The two components of the lens must be cemented together in order to avoid the loss of light by reflection on the air surfaces.

It is known that the optical conditions required can be actually fulfilled with two glasses cemented together keeping the systems achromatism by choosing conveniently the dispersive powers of the glasses.

Besides, considering selective action of the, atmosphere through which blue and purple light-is 'quickly absorbed, it is 'not necessary to conform of such rigorously to the achromatism condition. Practically it is possible, by using ordinary glass, to obtain a lens free from spherical aberration and from coma for the yellow radiations and sufficiently achromatic for its designed use.

With such lens, a good luminous field will readily be obtained with any plane mirror placed in the focal plane, provided that the incident pencil does not deviate too much from the pptical axis of the system.

But if the incident pencil deviates considerably from the axis the reflected pencil will be notably diminished in its intensity, due principally to a the lens.

However there is still two causes of loss of light for extra axial pencils: they are astigmatism and curvature of field of the image surface.

To lessen this defect the mirror'mustbe composed of a lens a (see Fig. 1) having the shape of a divergent meniscus metallized on its convex side, the concave one being turned towards the lens b. The convex side will have a radius of curvature equal to the focal length of the whole system and its apex will coincide with the focus of the whole.

The radius of curvature of the concave surface will be determined by the condition of giving to the curvature of the image surface the same value as that of the reflecting surface.

Instead of the catadioptrical disposition; which has just been described, sometimes a disposition simply catoptric can be used with advantage in -which the object-lens is replaced. by a mirror b of convenient dimensions. The apparatus shows then the arrangement represented on Fig. 2.

To reduce the divergency to its minimum, the.

mirror 17 must befree of spherical aberration (parabolic mirror, or Mangin mirror, for instance).

The diameter of the mirror 11 is determined by the field required for the sight; it will be chosen as small as possible so as not to stop too large a fraction of incident light. It may often happen that the field of positions which can be occupied by the source 0 ismore extended angularly in one direction (horizontal) than in the other (vertical). This circumstance can be used to reduce the dimension of the mirror 11' to what is strictly necessary to cover the whole extent of the-field of the image c. So the outline of the mirror a, instead of being circular, can be rectangular. 'In some cases, they may even be constituted by singly cylindrical reflecting plates.

Systematic introduction of a given divergency in the emerging pencil Every time that the purpose is not signaling at great distances, it is necessary to introduce systematically in the reflected luminous pencil, a

' certain divergency in order to render the signs vergency will be obtained either by leaving-a voluntary imperfection in the plane of the surfaces, or by placing a feebly divergent or convergent lens before each element, or when the trihedral is constituted by three surfaces .of a tetrahedron by giving to the fourth surface a shape slightly convex or concave or even simply irregular, as it can be directly. obtained by'molding.

When using the autocollimating element de- 1 rivedfrom the Fizeaus sight, the divergency is obtained by placing systematically the mirror in front or behind the focal surface of the objective system, byan amount easily determined by calculation or better empirically.

' of faces of any shape and the autocollimating elements, previously de- A feeble divergency is obtained when leaving optical aberration, notably spherical aberration in the autocollimating elements, which has besides the advantage of reducing considerably their cost.

As an example of autocollimating elements where spherical aberration is not especially corrected, we can point out:

1. Catoptrical elements previously described but in which the objective-mirrors areaffected with spherical aberration: we will take for instance simple spherical mirrors the quality of which need not be very good, like those obtained by bulging (glass) or stamping (metal).

2. A catadioptrical element in which the objective lens b and the mirror a are made of one single piece (see Fig. 3) by a lens whose limiting surfaces b and a are spheres, centered in d with their active surfaces, opposite. If r is the radius of curvature of the objective surface I); n, the refraction index of the substance from which the lens is formed, then the radius R of the re fleeting surface a will be Autocollimati ig reflecting surfaces In order to increase the luminous power of the autocolli'mating reflectors, we can enlarge their dimensions. This method presents however great inconveniences which are as follows:

1. From a certain diameter, the net cost rises much more rapidly than surface;

2. The weight of the instrument increaseslike power 3/2 of the luminosity. 3. The absorption of light in lenses grows very rapidly with their thickness, which is in proportion to their diameter, from which results a great reduction of luminosity. I

4. And again in a condition of optical action settled beforehand the length of the instrument is proportional to its diameter.

The method proposed in conformity with the invention, consists in increasing the luminosity the reflectors by constituting reflecting surextending by grouping scribed and having each the most economical dimension. With these conditions the price and weight of the instrument is proportionalto the luminosity required the thickness remaining constant.

The elements can be arranged to cover small or large surfaces so as to'form reflecting screens, or to form letters, drawings ,orany signs. I

We can also mount all the lenses in one and the same-support, and all the mirrors in another. the two supports being joined by crossbars of p a convenient length to bring the mirrors to focus,

a condition that can be obtained by adjusting the divergency to be introduced in the reflected pencil and by altering the distance from the lens to the mirror.

Catadioptric autocollimating surfaces can also beobtained. as shown in Fig. 5, by fixing on each side of a transparent plate e of convenient thickness, convex lenses 2: and a placing them on a sheet of glass, the objective lens on one side and the mirror on the other, the latter being 'metaltalized on its convex surface.

We can proceed in the same way in order to obtain catoptrical surfaces, by giving to the two lenses convenient radii of curvature and by metallizing the two on their convex surfaces (Fig. 6).

The autocollimating element can be placed on a shop window and to prevent the visibility of the mirrors from the outside, such mirrors may be coated with any opaque covering.

Finally, autocollimating refracting surfaces of any dimension and shape can be obtained by shaping of the surface of the autocollimating element of any type on transparent sheet (glass,

celluloid, cellophane) In the case of catadioptrical elements, the surfaces are obtained (see Fig. 7) by shaping plates of transparent substances so as to form on each surface a spherical apex with the radii r+R, indicated above, and directly opposite to each other. The value r+R, which ensures the concentricity of the spheres, is given to the thickness between apexes.

The waved surface formed by the mirror (1 is rendered reflecting by a suitable metallic deposit.

In the case of catoptr'ic elements, the surface constituting the mirrors a is metallized on a small area, on the mirror axis b, or the whole surface can receive a half transparent metallic deposit.

Very large autocollimating surfaces can be constituted by juxtaposition of smaller ones easier to obtain, as practiced for brick paving or covering of all kinds. Fig. 8 shows a disposition of this type, when on a tray is grouped a great number of systems of objective-mirror b-a.

Applications.The autocollimating elements derived from Fizeaus sight, previously described, those obtained by introducing divergency in Airys trihedral mirror, and the reflecting surfaces obtained by grouping autocollimating elements of any nature, are applicable in general to all sorts of optical signaling without its own source of light.

From those applications, the following are indicated as descriptive but not limited examples:

Optical teZegraphy.-Elements having very small divergency used alone or by group, operated by hand or provided with any mechanical appliance, allowing its use in a position having itself no source of light which could betray its presence so as to be able secretly to communicate with a lighting post situated very far away for instance an agent corresponding over the enemys camp; ships at sea corresponding between them or with I the coast; or an airship in optical communication with a post on the ground etc.

Optical signaling.-Signals of any sort can be constituted by autocollimating reflectors with more or less divergency and which appear luminous to those who are quite near a source of light for example:

Allrailway signals lighted by sources placed on engines, and behind which stand those who observe the track this eliminates dangers coming from accidental extinctions of the lamps; corner post indicators; dangerous descent; railroad crossings etc. placed along the roads in the country and which lighted by lanterns or search lights of wagons or cars, shine very brightly to the conductors eyes and impose themselves upon his attention.

Indicator names of streets, numbers of houses etc. readable at night by approaching any small luminous source in front of the eye: pocket electric lamp, flint, even an ordinary match.

Number placed .behind wagons or ships, train back lanterns, numbers placed in front of the engines.

Advertising-Advertising sign, placed along roads or railways legible at night'without special light and by simple reflection to the eyes of the travelers, of the almost totality of the light coming from lamps in the cars, can be constituted.

Marks placed on shop windows.

The invention is applicable to the construction of large fixed screens on which can be projected, by means of ordinary projecting lanterns, fixed or animated pictures, advertising signs legible by those persons who are near the lights ofa cafe for instance. On a screen of this description a plurality of pictures may be projected simultaneously from different sources and angles. signs although projected on the screen at the same time as those of a different character do not become confused one with the other as each sepa rate picture is only visible from the angle of projection.

Aviation.Autocollimating surfaces can be constituted which placed horizontally on the ground at intervals will giveat night to aviators flying above them useful indications, such as direction of the wind, with indications such as these it would not be necessary for an aerodrome to exhibit lighted signals. If the autocollimating elements are placed at exactly measured distances from each other, the aviator can determine his exact altitude above the ground at night,

These by means of any single stadimetric device and so may choose the exact moment for landing.

I claim:

1. An auto-collimating reflector comprising a glass unit formed at its two .ends with convex surfaces, the radii of the two surfaces being different but the centers of curvature of both being positioned in the same optical axis, the end portion with the curvature of smaller radius serving as an objective lens, and the end of larger curvature having in contact therewith means constituting a reflecting surface to serve as a concave reflector for the light entering the glass unit through the lens. 7,

' 2. An auto-collimating reflector in the form of a single block of glass having opposite convex surfaces centered in the same optical axis, one of the convex surfaces functioning as a lens and the other having in contact therewith means constituting a reflecting surface to form a concave mirror the principle focus of the lens being located substantially in the reflecting surface of the mirror.

3. An auto-collimating reflector in the form of a single block of glass having opposite convex surfaces of different radii but both centered in the same optical axis, one of the convex surfaces functioning as a lens and the other having in contact therewith means constituting a reflecting surface to form a concave mirror the principle focus of the lens being located substantially in the reflecting surface of the mirror.

4. An auto-collimating sight, comprising an obg objective lens of short focal length and an aligned smaller lens having its exterior surface a reflector and smaller than the objective, the radius of curvature of the objective lens being substantially equal to the focal length of the combination of the two lenses and the reflecting surface of the smaller lens lying substantially in the focal plane of the objective.

6. An auto-collimating sight, comprising an objective lens of short focal length secured to one face of a sheet of glass and a smaller lens secured to the opposite face of said sheet, the outer faces of both lenses being reflectors and the re flecting outer face of the smaller lens being substantially in the focal plane of the larger lens.

.7. An auto-collimating reflector, comprising an objective lens of short focal length attached to one side of a sheet of glass, an axiallyaligned glass mass attached to the other side thereof and having its outer convex face formed as a. reflector, the length of the optical axis between the convex surfaces of the lens and reflector being substantially equal to the focal length of the objective lens, the convex surfaces both being centered in this optical axis.

8. An auto-collimating reflector, comprising an objective lens of. short focal length attached to one side of a sheet of glass, an axially. aligned glass mass attached to the other side thereof and having itsouter convex face formed as a reflector, the length of the optical axis between the convex surfaces of the lens and reflector being sub-' stantially equal to the focal length of the objective lens, the convex surfaces both being centered in this optical axis, and the radius of curvature of the reflector being greater than the radius of .curvature of the lens.

9. An auto-collimating reflector, comprising an objective lens of short focal length attached to one side of a sheet of glass, an axially aligned glass mass attached to the other side thereof and having its outer convex face formed as a reflector, the length of the optical axis. between the convex surfaces of the lens and-reflector being substantially equal to the focal length of the objective lens, the convex surfaces both being centered in this optical axis, and the radius of curva- Reissue 0. 19,070.

It is hereby certified that HENRI kCHRETIEN errors appear in the printed specification of the above numbered patent requiring correction as follows: and 3 respectwely; for the words single block ture of the reflector being substantially equal to twice the radius of curvature of the lens.

10. An auto-collimating reflector, comprising a glass unit provided on one side with an objective lens of short focal length having a convex outer surface, and provided on the other side with 'an axially aligned convex reflectorthe outer surface of which is provided with means constituting a reflecting surface, the length of the optical axis between the convex surfaces of the'lens and reflector being substantially equal to the focal length of the objective lens and both convex surfaces being centered in this optical axis, the radius of curvature of the reflector being greater than the radius of curvature of the lens.

11. An auto-collimating reflector, comprising a glass unit provided on one side with an objective lens of short focal length having a convex outer surface, and provided on the other side with an axially aligned convex reflector the outer surface of which is provided with means constituting a reflecting surface, the length of the optical axis between the convex surfaces of the lens and reflec'- tor being substantially equal to the focal length 100 of the objective lens and both convex surfaces being centered in this optical axis, the radius of curvature of the reflector being substantially equal to twice the radius of curvature of the lens.

12. An auto-collimating sight comprising a glass body portion having an objective lens of short focal length on one side thereof and an axially aligned reflecting lens on the other side thereof, the curvature of the reflecting lenshaving a radius equal to the focal length of the combination of the two lenses, the reflecting lens having its outer face provided with means constituting a reflecting surface.

13. Anauto-collimating reflector in the form of a unit of glass provided with means constituting a plurality of adjacently arranged pairs of opposite convex surfaces, the surfaces of each pair being centered in the same optical axis, one of the convex surfaces of each pair functioning as a lens and the other having in contact therewith means constituting a reflecting surface to form a concave mirror, the principal focus of the lens being located substantially in the reflecting surface of the'mirror.,

HENRI CHRE'IYIEN.

Certificate of Correction February 6', 1934,

Page lines 127 and 136, claims 2 read amt; and that the said Letters Patent'should be read with thesev corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this am; day of November, A. b.1936.

VAN ARSDALE, r i Actmg Commissioner of Patents. 

